1. Field of the Invention
The present invention relates to methods of forming thin copper films and semiconductor devices with thin copper films, and particularly to a method of forming a thin copper film on an underlying film including metal with high melting point or nitride thereof by means of CVD (Chemical Vapor Deposition), and a semiconductor device with the thin copper film.
2. Description of the Background Art
Conventionally, material of A1 with copper added thereto having high resistance or electromigration resistance has generally been used as interconnection material for an LSI (Large Scale Integration). However, as LSIs are increasingly reduced in size to achieve as small an interconnection width as about 0.15 .mu.m or less, a problem associated with resistance or the like becomes inevitable even if material of A1 with copper added is employed for interconnection.
Then, to cope with the interconnection width of about 0.15 .mu.m or less, which will be expected in future, employment of a copper interconnection is considered. Copper is relatively easily diffused, so that it might disadvantageously be diffused in the underlying film by thermal treatment commonly performed in a manufacturing process of the LSI. To avoid such diffusion, a common practice would be to form a diffusion barrier film such as a TiN film under the copper interconnection.
In view of the foregoing, a conventional method of forming a thin copper film on a TiN film will now be described with reference to FIGS. 10 and 11. FIGS. 10 and 11 are cross sectional views showing first and second steps of the conventional method of forming the thin copper film on the TiN film. FIGS. 10 and 11 show a thin copper film 4 formed on a TiN film 3, which has been formed on a silicon substrate 1 with a silicon oxide film 2 interposed.
Referring now to FIG. 10, silicon oxide film 2 and TiN film 3 are sequentially deposited on silicon substrate 1 by means of CVD, for example. Then, as shown in FIG. 11, thin copper film 4 is formed on the TiN film by means of CVD using for example Cu (hfac) (tmvs) without any particular pretreatment. Here, hfac and tmvs are abbreviations of hexafluoroacetylacetonate and trimethylvinylsilane, respectively.
When thin copper film is formed on TiN film 3 using Cu (hfac) (tmvs) by means of CVD without any pretreatment as mentioned above, however, sufficient adhesion is not ensured between thin copper film 4 and underlying TiN film 3 as pointed out in Advanced Metalization for ULSI Applications, pp. 79-86, 1994.